Electrical measuring-instrument



(No Mbd'el.) 2 Sheets-Sheet 1. E. WESTON. ELECTRICAL MEASURING INSTRUMENT.

Patented Au (No Model.) 2 Sheets-Sheet 2,

v E. WESTON. ELEOTRIGAL MBASURINQINSTRUMBNT. No. 480,899.

Patented Aug 16, 1892.

\xl wNxxxx a M m u a INVENTOI? pm UNrTED STATES PATENT OFFICE.

EDWARD WESTON, OF NEWVARK, NEW JERSEY.

ELECTRICAL MEASURING-INSTRUMENT.

SPECIFICATION forming part of Letters Patent No. 480,899, dated August 16, 1892. Application filed February 19, 1892. Serial No. 422.082- (No model-i To all whom it may concern.-

Be it known that I, EDWARD WESTON, of Newark, Essex county, New Jersey, have in- Ven tedanew and useful Improvement in Electrical Measuring-Instruments, of which the following is a specification.

My invention relates to an instrument more particularly intended for use as an ammeter for measurement of current strength.

My 1nvention consists in the construction and arrangement of the movable coil and the POIQPIGCGS of the magnet, the said coil being so disposed that it surrounds an interior ringshaped or substantially tubular pole-piece, along which it moves bodily, thereby traverslng a very powerful field of force produced between the inner pole-piece and a suitablycurved inclosing outer pole-piece.

My invention further consists in the novel construction of the inner pole-piece of the magnet.

In the accompanying drawings, Figure l is a front view with certain parts broken away to show the interior of the instrument. Fig. 2 is a section on the line X X of Fig. 1. Fig. 3 is a section on the line X X of Fig. 4. Fig. 4. is a section on the line Y Y of Fig. 3. Figs. 3 and 1 show parts on a larger scale than do Figs. 1 and 2.

Similar numbers and letters of reference indicate like parts.

1 is the case of theinstrument, preferably circular in form, provided with a back or base 2, the glass covering-plate 3, and the holdingring 4 for said glass plate.

Within the case 1 and supported upon the back plate 2 is an electro-magnet of substantially the shape as that which is fully shown and described in Letters Patent No. 446, l93, granted to me February 17, 1891. This magnet consists of a cylindrical box or case formed by two annular disks 5, the rear one of which (not shown) is secured to the base-plate 2. Between said disks 5 is received the peripheral wall 6. The rear disk 5 corresponds to the disk G in my aforesaid Letters Patent, and in substantially the same way supports a cylindrical pole-piece 7, which corresponds to the pole-piece E in said patent. The outer disk 5 is made with a circular flange or collar 8 around its central opening corresponding to the part D in my said patent. The pole-piece 7 therefore extends through the cylindrical box or case formed by the disks 5 and periphery 6 and is received within the pole-piece 8.

Inserted in the pole-piece 7 is a copper core 9, perforated longitudinally and surrounded by a sheath of insulating material 10, by which said core is insulated from the magnet structure.

Extending through the sides of the polepiece 7, in the manner fully described in my aforesaid prior patent, are the ends of a number of copper strips 11,which are electrically connected to the core 9. The copper strips are wound parallel to one another around the core 9 and pole-piece 7 and form a fixed coil between the turns of and surrounding the exterior of which are layers of insulating material, as 12. The copper core connects in any suitable way with a metallic terminal 13 outside of the case. The outer ends of the strips 11 communicate with another terminal 14, also outside of the case. The current therefore, entering either binding-post 13 or 14, will proceed through the copper strips and core to the other binding-post. 1 preferably employ this arrangement of large copper strips and core because I intend this particular instrument for use as an ammeter in the measurement of currents of great strength, although, of course, by suitable change in winding it can be used as a voltmeter.

I desire now to call particular attention to the construction of the pole-piece 7, which pole-piece, as I have said, corresponds in position and general arrangement to the polepiece E of my aforesaid prior patent; but on comparing the two it will be noticed that the pole-piece E in said prior patent is in itself completely cylindrical, whereas the pole-piece 7 forms a cylindrical sleeve around the core 9 and is provided with an oifset or arm 15, which extends into the cylindrical opening Within the pole-piece S. The portion of the arm 15 which enters said opening has attached to it parts which together make up a cylindrical pole-piece, so that, in fact, there are present two cylindrical pole-pieces, one of which 7 surrounds the core 9 and the other which are supported by the arm 15 consist,

first, in a cylinder 16, which has a longitudinal slit or opening of such a width that the edges of this opening meet the edges of the arm 15, as indicated at the points a, Fig. 4; second, there is another cylinder 17, which fits accurately upon the exterior of the cylinder 16, and which is also provided with alongitudinal slot at b, Fig. 4. The width of this slot is such that the cylinder 17 can be received upon and supported by the arm 15, as shown in Fig. 4:. Now the cylinder 17 is secured to the arm 15 by screws 18, (dotted lines,) and the cylinder 16 is secured to the cylinder 17 by screws 19, (dotted lines.) The reason for this construction will be explained farther on. It is sufficient here to call attention once more to the fact that the cylinders 16 and 17, connected together and being constructed in the manner described, offer what is practically a shouldered opening, into which the supporting-arm 15 en ters, and that by taking out the screws 18 and 19 these cylinders 16 and 17 may be separated from one another and from the arm 15. It is also necessary to direct particular notice to the construction of the pole-piece 8. In my prior patent, No. 446,493, this is a simple cylinder or cylindrical flange; but, as shown best in Fig. 4, in my present instrument the pole-piece 8 is not a complete cylinder, but has a longitudinal slot on its upper side at c. The object of this opening will be described fart-her on.

Referring now to Fig. 3, on the under side of the arm 15 are secured brackets 20 and 21. These brackets carry jewels, which serve as supports for the pivoted arbor 22. Connected each at one end to the arbor 22 are coiled springs 23. The outer ends of said coiled springs 23 are fastened to bent arms 24, which are pivoted to the exterior of the brackets 20 and 21. This arrangement of coiled springs and bent arms has been so often described by me in prior patents-as, for example, No. 392,387, granted to me November 6, 1888* that further description of it other than to state that by turning the arms 24 the tension of the springs 23 may be adjusted as desired and that said springs oppose the movement of the coil now to be described.

Supported upon the arbor 22 are two forked arms 25. These receive between them a light frame 26, of paper or aluminium, (preferably of metal,) upon which is wound a coil of fine insulated wire 27, Fig. 1. The frame loosely incloses the cylinders 16 and 17, and also, as

- is obvious, passes through the annular space between the outer periphery of cylinder 17 and the inner periphery of pole-piece 8. Now as the cylinder 17 is one pole of the magnet and the pole-piece 8 is the other it follows that there must be a very intense field of force between the above-named surfaces, and it is also apparent that the arrangement of the coil 27 is such that it intersects the lines of this field of force. As the coil is supported on the frame 26 and the frame 26 is supported on the arbor 22, it will be clear that when the coil is moved in the annular field above named the arbor 22 will be rotated, and the movement of this arbor will be opposed by the constant resistance of the volute springs 23.

Supported on the frame 26 is an index needle or pointer 28, which extends through an opening in a scale-plate 29. This scale-plate is marked in amperes or other suitable units.

I have already described one circuit in the instrument, whereby the current to be meas- 'ured is led through the copper strips 11,forming the fixed coil. By this means an intense magnetic field is produced in the annular space between the pole-pieces, in which the movable coil 27 is arranged. At the same time a portion of said current in shunt circulates through the coil 27. This shunt-circuit is indicated in Fig. 3, the current entering, for example, by the Wire d, thence passing to the pivoted arm 241:, spring 23, one arm 25, through the coiled spring 23, shaft 22,0ne of the arms 25 to the coil 27 through the other arm 25 to the other spring 23, the other pivoted arm 24, and finally through the wire e. Insulation of these parts is to be arranged to allow of this circuit. The current passing through the coil 27 will produce, of course, a field around said coil.

In accordance with well known laws the mutual interaction of the field surrounding the coil and the field produced between the pole-pieces in which the coil is located will cause a bodily movement of the coil and a consequent rotation of the shaft 22. The extent of movement of the coil 27 will bear a relation to the difference of potential in the current between the terminals of the instrument, or as the instrument is here shown constructed to the strength of the current traversing them. The extent of said movement is shown by the travel of the needle 28 over the scale 29 in the usual way.

In view of the foregoing explanation of the operation of the apparatus, the reasons for the construction of the pole-pieces will become evident. The cylinders 16 and 17 are slit or slotted, so as to allow the frame 26 to be put upon them by being inserted through the openings. The reason for using two cylinders-namely, 16 and 17-instead of making these two parts in one piece with a shouldered opening cut in them for the reception of the arm 15, is to secure simplicity and cheapness of construction. It would obviously be a difficult thing to mill a shouldered recess, as at a, in the edges of a longitudinal slot made in a hollow cylinder, and it would be necessary to have recourse to hand-filing, which would be obviously expensive. By using two cylinders 16 and 17 I can make each separate on the lathe, turned perfectly true, so that they will be an accurate fit, and by simply cutting the longitudinal slot in one wider than the longitudinal slot in the other I produce when these two cylinders are put to- IIO gether as shown the shouldered opening accurately fitting upon the arm 15.

The object of the opening in the polepiece 8 is obviously for the purpose of preventing leakage of magnetic lines across the space not traversed by the coil and also to allow access to the screws 18 and 19, so as to allow the parts to be taken asunder without dismounting the entire apparatus... The threaded rod 30 on the back of the case is in tended to receive a nut for the purpose of securing theinstrument to a partition or other solid support.

I claim 1. In an electricalmeasuring-instrument, a magnet having concentric poles, the inner pole being substantially tubular or ring-shaped and the outer pole curved around the periph ery of the inner pole, and a movable coil extending through said inner pole and through the space between said poles.

2. In an electrical measuring-instrument, a magnet havingconcentric poles, the inner pole being substantially tubular or ring-shaped and the outer pole curved around the periphery of the inner pole, a shaft or arbor supported within said inner pole, and a coil carried by said shaft and extending through the space between said poles.

3. In an electrical measuring-instrument, a magnet having concentric poles, the inner pole being substantially tubular or ring-shaped and the outer pole curved around the periphery of the inner pole, a movable coil extending through said inner pole and through the space between said poles, and an index or pointer carried by said coil.

4. In an electrical measuring-instrument, a magnet having concentric poles, the inner pole being substantially tubular and the outer pole curved around the periphery of the inner pole, bearings secured within said tubular pole, a shaft or arbor journaled in said bearings, and a coil carried by said shaft and extending through the space between said poles.

5. In an electrical measuring instrument,a magnet having concentric p0les,,the inner pole being substantially tubular and the outer pole curved around the periphery of the inner pole, bearings secured within said tubular pole, a shaft journaled in said bearings, a coil carried by said shaft and extending through the space between said poles, a fixed scale, and

an index or pointer carried by said coil and extending over said scale.

6. In an electrical measuring-instrument, a magnet having concentric poles, the inner pole being substantially tubular or ring-shaped, and the outer pole curved around the periphery of the inner pole, a movable coil extending through said inner pole and through the space between said poles, and a spring opposing the movement of said coil.

7. In an electrical measuring-instrument, a movable coil, a magnet, and a detachable curved pole-piece for said magnet, upon which pole-piece said coil is received and freely moves.

8. In an electrical measuring-instrument, a movable coil, a magnet, and a detachable curved pole-piece, the extremities of said polepiece being separated for a space sufficient to allow said coil to pass upon the body of said pole-piece.

9. In an electrical measuring-instrument, a movable coil, a magnet having a fixed projecting pole-piece, and a detachable curved pole-piece, upon which said movable coil is received, the said fixed pole-piece entering and closing the opening between the extremities of said curved pole-piece.

10. The combination, with the curved extremity 15, of a magnet pole-piece, and the cylinder 16, having a longitudinal slot or opening receiving said extremity 15.

11. The combination, with the curved extremity 15, of a magnet pole-piece, the cylinder 16, having a longitudinal slot or opening receiving said extremity 15, and the exterior slotted cylinder 17, surrounding said extremity l5 and cylinder 16.

12. In an electrical measuring-instrument, a magnet havingacurved pole-piece 15, the cylinder 16, having a longitudinal slot or opening receiving said pole-pole, and a coil 27, received and movable around said cylinder 16.

13. In an electrical measuring-instrument, a magnet having a curved po1e-piece15, the cylinder 16, having a longitudinal slot or opening receiving said pole-piece, the inclosing slotted cylinder 17, and a coil 27, received and movable upon said cylinders 16 and 17.

EDWARD WESTON.

Witnesses:

H. R. MOLLER, M. Boson. 

